-LRB- CNN -RRB- -- Low visibility caused by mist and sand created poor flying conditions for the pilot of an Afriqiyah Airways flight that crashed just before landing in Tripoli , Libyan sources with knowledge of the investigation said Saturday .

The plane , an Airbus A330-200 , originated in Johannesburg , South Africa , and was at the end of its nearly nine-hour flight when it crashed Wednesday . All but one of the 104 passengers on board were killed .

The sources said that as the pilot approached Tripoli International Airport , he took the plane off auto-pilot hoping to manually land the aircraft . He realized he was in trouble and tried to pull the plane up and turn the auto-pilot back on to give it another try , the sources said .

But the effort was too late and the plane slammed violently into the ground , explaining the condition of the wreckage and damage to the plane 's tail at the crash site , the sources said .

An investigation into the crash is under way , and authorities are reviewing the aircraft 's flight data recorder .

Meanwhile Ruben van Assouw , the 9-year-old sole survivor of the plane crash , has returned home to the Netherlands .

He suffered multiple fractures to his legs and underwent surgery at Al Khadra Hospital , said a doctor at the hospital who declined to give her name .

Both of Ruben 's parents and a brother were killed in the crash , a Dutch foreign ministry representative said .

Ruben 's family issued a statement Friday expressing gratitude to people who have helped them , such as Libyan hospital professionals and Dutch envoys , as well as the outpourings of sympathy from citizens in both countries .

The family also thanked `` the vast majority of the Dutch media for respecting our privacy . ''

The family , which will raise Ruben , said the boy knows that his parents and brother were killed .

`` Considering the circumstances , Ruben is doing fine . He is sleeping a lot ; now and then he wakes up and is then lucid , '' the family said in the statement . `` He has drunk a little , and has seen the flowers and cuddly toys . ''

Ruben 's family said it has to deal with `` two kinds of grief '' -- the sorrow the boy is enduring and the sadness over the loss of the other family members .

`` The coming period will be very difficult for us , '' the family said . `` We hope that all the media will respect our privacy . ''

More than two-thirds of the passengers killed in the plane crash were Dutch , the ministry said .

Passengers from Libya , South Africa , Belgium , Austria , Germany , France , Zimbabwe and Britain were also among the victims , the airline said on its Web site . The Dutch foreign ministry said Friday it is sending more experts to Tripoli to help Libyan authorities and Dutch colleagues identify the victims .

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Sources : Mist and sand created poor flying conditions for the pilot of crashed plane

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Family says 9-year-old sole survivor knows his immediate family were killed in plane crash

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Dutch foreign ministry sending experts to Tripoli to help authorities identify victims